Analytical Design and Assurance of Digital Flight Control System Structure

Abstract

With the increasing prevalence of flight-critic al functions, sophisticated fault tolerance, and functional integration in digital flight control systems (DFCSs), purposeful design of system structure can no longer be neglected, Needed then are criteria and methods to obtain good system structure, which is a prerequisite to good flight software structure. Basically, this calls for a new awareness in the flight controls community of a distinct and coherent body of techniques for the analytical design of structure that is comparable with that now used for the analytical design of control laws. In the software community, it calls for a recognition that the characteristics of redundant, real-time, closed-loop digital systems demand rather specialized methods that transcend strictly software issues. An exacting, practitioner-oriented methodology has been developed that enables the analytical design of DFCS structure essentially independent of control law development. Utilizing control state decomposition, the methodology is based on a design paradigm that facilitates analytical design verification in the form of consistency, completeness, and reachability checks. Heavy emphasis is also placed on quantitative methods to control design and implementation complexity and on tradeoff techniques to enhance the ilities from the outset of design.